RICHARDS AND PARKER. — ATOMIC WEIGHT OF MAGNESIUM. 63 



duced silver was fused on a cupel of sugar charcoal before the blowpipe. 

 The resulting button was scrubbed witli sand, and made the anode of a 

 weak galvanic circuit in a solution of argentic nitrate prepared from the 

 same silver. The cathode was a piece of pure silver wire, upon which 

 the whole of the silver was deposited iu a crystalline mass. The silver 

 crystals were then removed from the solution and fused in a vacuum 

 upon a boat of pure lime,* which was contained in a porcelain tube. 

 Such a boat may be made by lining a porcelain boat with a mixture of 

 three parts of pure lime and one part of pure anhydrous calcic nitrate, 

 and igniting the mixture. The i)orcelaia boat is thus covered with a 

 firm, coherent layer of pure calcic oxide. In order to prevent the pos- 

 sibility of a trace of organic matter distilling off from the rubber stoppers 

 usually used to close sucli a tube, a set of hollow brass stoppers were 

 made, through which a current of cold water circulated. This latter 

 device is due to a suggestion of Professor Henipel. The construction of 

 this piece of apparatus is evident from the diagram. 





<-N 



°t.-5^ 



j^ 





es^2^^^ ^ 



Fig. 2. Apparatus for Fusing Silver, Vertical Section. 



A is connected with Sprengel pump. B B = hollow brass stoppers in porcelain 

 tube. C = boat of lime containing silver. D =r " window " for observation. 

 E E E E = rubber packing of stopper. F = Fletcher furnace. 



Of course the button after fusion showed no trace of spirting from con- 

 tained oxygen. It was scrubbed with distilled water and clean sand, 

 and divided into small pieces by means of a clean steel chisel. The 

 fragments were alternately boiled in strong hydrochloric acid and digested 

 in ammonia water, this process being repeated ten or fifteen times. The 

 silver was finally washed with distilled water and afterwards kept in a 

 desiccator, which was opened only when necessary to weigh out silver 

 for a determination. 



A portion of the second sample was treated in the same way, except 

 that in the end it was fused on sugar charcoal before the blowpipe and 



* These Proceedings, XXX. 379; XXXI. 173. 



